nastran

1. odd; eccentric; weird
   Njegov komšija je pomalo nastran, ali je bezopasan. — His neighbour is a bit odd, but harmless.
   Stari slikar je bio nastran i retko je razgovarao s ljudima. — The old painter was eccentric and rarely talked to people.
2. derog. perverse; perverted; sick
   To je nastrana ideja, samo bolestan um tako misli. — That's a sick idea, only a twisted mind thinks like that.

In modern usage the word is usually understood in sense 2, 'perverted', especially of sexual tendencies; the 'eccentric' sense is rarer and can sound ambiguous without context (čudan, osobenjak are neutral alternatives).